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07.21.14 PALAU: PICRC conducts research to assess the impact of the El Niño on Palau’s reefs

An El Niño Southern Oscillation (ENSO) event, also known as El Niño, is predicted to continue to develop throughout this
summer and into 2015. In Palau, this phenomenon leads to severe droughts and high seawater temperatures. The result
of abnormally high water temperature, from weeks to months, causes corals to bleach.

Photo: PICRC

When the seawater temperature is above a threshold, most corals no longer cope with the temperature stress, and
release their symbionts. Losing their symbionts not only makes corals appear completely white, but this loss also deprives
corals of their major food source. Symbionts photosynthesize and supply corals with food. Most corals will die of
starvation after losing their symbionts. The last global bleaching event happened in 1998, as a result of an ENSO event,
although a smaller, regional bleaching event also occurred in 2010.
From June to July 2014, the PICRC research team conducted a survey to assess the status of Palau’s reefs at their 22
permanent monitoring sites. This survey was purposefully done before a possible bleaching event. These underwater
surveys followed the standardized monitoring protocol, recording data on benthic cover (photo quadrats) and on the
abundance and size estimates of fishes and invertebrates. Throughout the entire summer period, PICRC also closely
monitored seawater temperature using underwater data loggers.
In case of the occurrence of a bleaching event, which is expected in late July to early August in 2015, PICRC will do a
large scale, rapid survey of 80 sites during the bleaching event to assess where and which corals bleach. Follow-up
surveys will be conducted at the 22 permanent sites will be conducted after the bleaching event to examine mortality and
recovery from bleaching. Data collected will help the researchers understand the effects of a bleaching event on the
whole reef community, including invertebrates and fishes, in Palau.
At a time of rapid global climate change, ENSO events accompanied with the occurrence of abnormally high seawater
temperature are predicted to occur more frequently and intensely. Therefore, it is essential to understand where corals
bleach, and which corals die or recover, during these events. Judging by the last ENSO event, it has been shown that
some reefs around Palau are more temperature tolerant than others, and are therefore more adapted to survive in waters
with higher temperature. The research by PICRC will help to identify where these temperature-tolerant reefs are located
in Palau so that they can be given special focus for protection. These special areas might hold the key to our reefs
survival in an increasingly warming world.